I think Imran's position in all time xi is in doubt only if you want to go with four frontline bowlers plus sobers as the fifth option (and the no.6 batsman). even in that case, he is on par with Marshall, Hadlee, McGrath, Ambrose and Steyn to be the primary fast bowler; marginally ahead of other great options that complete the top 10 pacemen: Truman, Lillee, Barnes and Akram. When you add his batting to the equation, his selection is almost a no brainer.
If your team is from the post Sobers era, or if Sobers is playing as the third middle order bat and the six bowler, then the team sheet should start with Imran's name. Anyways, Imran in an ATG XI is a shoo-in by all standards.